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A-Level Biology OCR A

Blood Plasma Basement Membrane Glomerulus Arteriole Passes Cells

Ultrafiltration is driven by high pressure in glomerular capillaries, forcing plasma fluid through capillary walls and basement membranes. Blood cells and large proteins are retained due to their size, while podocytes prevent any that manage to pass from entering the nephron. The filtrate, containing substances like glucose, salt, and urea, has a similar concentration to blood plasma.

Ultrafiltration involves blood entering the glomerulus via the afferent arteriole and leaving via a narrower efferent arteriole, creating high pressure. Plasma is forced out through the capillary walls and basement membrane, with cells and large molecules like proteins retained. Podocytes with pedicels prevent filtered cells and proteins from entering the nephron. The resulting filtrate contains glucose, salt, and urea at concentrations similar to blood plasma.

Front Describe the process of ultrafiltration
Back Glomerulus & Bowman's capsule:
  • Glomerulus supplied with blood from afferent arteriole
  • Blood leaves through a narrower efferent arteriole leading to considerable pressure in the glomerular capillaries
  • Blood plasma is forced out through capillary wall which acts like a sieve
  • Fluid passes through the basement membrane (second sieve)
  • Most of plasma contents pass through basement membrane but blood cells and large molecules (eg proteins) are retained bc of size
  • Filtrate passes into the nephron through slits between the pedicels of footed cells called podocytes (prevents any cells, platelets or large plasma proteins that got through basement membrane are stopped)
  • The filtrate is a solution of glucose, salt, urea and other substances - same conc as blood plasma

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